Drive unit and drive module

ABSTRACT

A drive unit and drive module which use a shape memory alloy as a drive source to move a driven member, and which can drive at a high speed, independently of the ambient temperature and the position of the driven member. The timing of moving the driven member is controlled based on the position to which the driven member is moved, and based on the settling time for the driven member moved to that position to settle at that position, thus, the driven section can be moved in the minimum drive time, and this arrangement provides the drive unit and drive module that can drive at a high speed, independently of the ambient temperature and the position of the driven member.

This application is based on Japanese Patent Application No. 2007-122159filed on May 7, 2007, in Japanese Patent Office, the entire content ofwhich is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a drive unit and drive module,particularly to a drive unit wherein a shape memory alloy is used as adrive source.

BACKGROUND

In recent years, the digital camera function comes standard with thepersonal device typically represented by the mobile phone. Further,there has been an increasing demand based on the social demand for asmall-sized monitoring camera. This has created a heavy demand forfurther reduction in the size and weight of a camera module. In themeantime, the camera module used in the personal device or small-sizedmonitoring camera is required to meet the demands for more and moresophisticated functions such as an auto-focusing function and imagestabilization function.

An actuator for driving the optical system and mechanical system isessential to ensure sophisticated functions of the camera module. Thisrequires an actuator capable of providing sophisticated functions whilemeeting the demand for more compact and lightweight configuration.

In this situation, an actuator using a shape memory alloy attractsattention as an actuator providing sophisticated functions while meetingthe demand for more compact and lightweight configuration. The shapememory alloy is typically represented by a titanium-nickel alloy, andcan be defined as the alloy that, after having been subjected todeformation below a predetermined temperature, comes back to theoriginal status due to martensite transformation by raising thetemperature above that temperature level. This property of the alloy isutilized to provide the performance of the actuator by heating.

In the shape memory alloy having such excellent properties, the drivingprinciple is based on temperature. Thus, the characteristics of theshape memory alloy tend to depend on the ambient temperature, and itneeds to be controlled by detecting the ambient temperature, when it isput into practical use.

One of the techniques proposed so far in the field of the catheterwherein the shape memory alloy is used as an actuator, for example, is amethod of detecting the ambient temperature using a temperature sensorsuch as a thermistor installed in addition to the shape memory alloy(Unexamined Japanese Patent Application Publication No. H06-114003).

However, the technique proposed in the Unexamined Japanese PatentApplication Publication No. H06-114003 uses a temperature sensor such asa thermistor installed in addition to the shape memory alloy. Thisarrangement requires a space for the temperature sensor, and is notsuited to meet the requirements for downsizing. This technique alsorequires an additionally installed temperature detecting circuit fordetecting the temperature using the temperature sensor, which means thatthe technique requires an increased space and much more number of parts,with the result that a substantial cost increase will occur. Further,due to the geometric and spatial restrictions, it may not possible toplace the temperature sensor close to the shape memory alloy, and thismay result in poor precision of detection of the temperature.

SUMMARY

The present invention has been created in order to resolve theseproblems with the conventional art. An object of the present inventiontherefore is to provide a drive unit and drive module wherein a shapememory alloy is used as a drive source, and high-precision detection ofthe ambient temperature of the shape memory alloy is realized withoutinstalling a separate temperature sensor.

In view of forgoing, one embodiment according to one aspect of thepresent invention is a drive unit, comprising:

a shape memory alloy which is configured to move a driven member, whichis biased in a first direction, in a second direction different from thefirst direction when the shape memory alloy is supplied with electriccurrent;

a drive section for supplying the shape memory alloy with electriccurrent;

a shape memory alloy resistance calculating section, for calculating aresistance of the shape memory alloy when the shape memory alloy issupplied with the electric current by the drive section,

a status detection section for detecting a status of the shape memoryalloy based on the resistance of the shape memory alloy calculated bythe shape memory alloy resistance calculating section,

a control section for controlling, based on a detection result of thestatus detection section, the drive section to control the shape memoryalloy to move the driven member.

According to another aspect of the present invention, another embodimentis a drive module, comprising:

a driven member which is biased in a first direction;

a shape memory alloy which is configured to move the driven member in asecond direction different from the first direction when the shapememory alloy is supplied with electric current;

a drive section for supplying the shape memory alloy with electriccurrent; and a shape memory alloy resistance calculating section, forcalculating a resistance of the shape memory alloy when the shape memoryalloy is supplied with the electric current by the drive section,

a status detection section for detecting a status of the shape memoryalloy based on the resistance of the shape memory alloy calculated bythe shape memory alloy resistance calculating section,

a control section for controlling, based on a detection result of thestatus detection section, the drive section to control the shape memoryalloy to move the driven member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representing an example of the image pickupapparatus as a first embodiment of the present invention;

FIGS. 2 a, 2 b and 2 c are schematic diagrams showing an example of themajor structure of an AF mechanism;

FIGS. 3 a and 3 b are schematic diagrams showing the relationshipbetween the SMA and a drive arm;

FIGS. 4 a, 4 b and 4 c are schematic diagrams showing the relationshipbetween the feed-out distance of the imaging optical system and thecharacteristics of the SMA;

FIGS. 5 a and 5 b are schematic diagrams showing the relationshipbetween the feed-out distance of the imaging optical system and theresistance of the SMA;

FIG. 6 is a block diagram showing an example of the circuit structure ofthe SMA driving section;

FIG. 7 is a diagram representing the main routine of the flow chartshowing the flow of the movement of the image pickup apparatus;

FIG. 8 is a flow chart showing the Step S200 “status detectionsubroutine” of FIG. 7;

FIG. 9 is a flow chart showing the Step S600 “SMA status detectionsubroutine” of FIG. 8;

FIGS. 10 a and 10 b are drawings showing an example of the ambienttemperature table;

FIG. 11 is a flow chart showing the Step S300 “lens infinite positionsetting subroutine” of FIG. 7;

FIG. 12 is a flow chart showing the Steps S500 “lens drive subroutine”of FIGS. 11 and 15;

FIGS. 13 a and 13 b are schematic diagrams showing the settling time;

FIG. 14 is a diagram showing an example of the settling time table;

FIG. 15 is a flow chart showing the Steps S400 “AF subroutine” of FIG.7;

FIG. 16 is a schematic chart showing the hysteresis between the feed-outposition and the target SMA resistance when the imaging optical systemis fed out and fed in;

FIG. 17 is a schematic diagram representing an example of the hysteresiscorrection table;

FIGS. 18 a and 18 b are schematic diagrams representing the shutter unitas a second embodiment of the present invention;

FIG. 19 is a flow chart showing an example of the flow of the operationswhen the shutter unit is used in a digital camera;

FIGS. 20 a and 20 b are schematic diagrams representing an imagestabilization function as a third embodiment of the present invention;and

FIG. 21 is a flow chart representing an example of the flow of theoperation when the image stabilizing unit is used in the image pickupapparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is described based on the illustrated embodimentswithout being restricted thereto. The same or equivalent portions asthose in the drawings will be assigned to the same numerals ofreference, and will not be described again.

In the first place, a first embodiment of the present invention will bedescribed with reference to FIGS. 1 through 17. FIG. 1 is a blockdiagram representing an example of the image pickup apparatus as thefirst embodiment of the present invention.

In FIG. 1, an image pickup apparatus 10 is a camera module built in amobile phone, for example, and includes an imaging optical system 201,automatic focusing (hereinafter referred to as “AF”) mechanism 100, andcamera circuit 300. The camera circuit 300 contains an image pickupdevice 301, image pickup section 320, control section 310, storagesection 340, SMA driving section 330 and others. The image pickupapparatus 10 is a drive module of the present invention, and the AFmechanism 100 and camera circuit 300 serves as a drive unit of thepresent invention.

The imaging optical system 201 forms an optical image of a subject onthe imaging surface of the image pickup device 301. The AF mechanism 100adjusts the focus by moving the imaging optical system 201 in thedirection of an optical axis 203. The AF mechanism 100 is provided witha wire-shaped shape memory alloy (hereinafter referred to as “SMA”) as adrive source for moving the imaging optical system 201. The AF mechanism100 will be described with reference to FIGS. 2 a, 2 b and 2 c andbeyond.

The optical image of the subject formed on the imaging surface of theimage pickup device 301 is subjected to photoelectric conversion by theimage pickup device 301, and is converted into the digital image data bythe image pickup section 320. The image data prior to image capturingoperation is displayed as a moving image for previewing on the displaysection 999 through the control section 310. The captured image data isstored in a storage section 340 comprised of memories and others,through the control section 310, and is displayed as a captured image onthe display section 999 when required. The display section 999 can berepresented by the liquid display screen of a mobile phone, for example.

The image pickup section 320 controls the operation of the image pickupdevice 301 to obtain the aforementioned image data. In collaborationwith the control section 310, the image pickup section 320 performs theprocess of focus detection to get focus information (hereinafterreferred to as “AF data AFD”), using the image data of the pixels(hereinafter referred to as “AF pixels”) located in part of the area(hereinafter referred to as “AF area”) on the imaging surface of theimage pickup device 301.

The SMA driving section 330 provides the control of current supply tothe SMA, whereby the drive of the AF mechanism 100 is controlled. TheSMA driving section 330 moves the imaging optical system 201 in thedirection of the optical axis 203, whereby the focus of the imagingoptical system 201 is adjusted. The SMA driving section 330 will bedescribed in details with reference to FIG. 6. The aforementioned focusdetection together with focus adjustment will be referred to as an AFoperation.

The control section 310 is made up of a microcomputer and others, andcontrols the imaging operation by the aforementioned image pickup device301 and image pickup section 320, and the overall operation of the imagepickup apparatus 10 including the AF operation. The control section 310can be a microcomputer that controls equipment, such as a mobile phone,incorporating the image pickup apparatus 10.

The following describes the structure and operation of theaforementioned AF mechanism 100 with reference to FIGS. 2 a, 2 b and 2 cand FIG. 6. FIGS. 2 a, 2 b and 2 c are the schematic diagrams showing anexample of the structure and operation of the major components of the AFmechanism 100. FIG. 2 a is a top view of the AF mechanism 100 takenalong the plane A-A′ perpendicular to the optical axis 203 of FIG. 2 b.FIG. 2 b is a side view of the AF mechanism 100 as viewed from directionB in FIG. 2 a.

In FIGS. 2 a, 2 b and 2 c, the AF mechanism 100 is made of a base plate101, top plate 103, SMA support member 105, lens barrel 111, lens driveframe 113, SMA 151, tension guide 153, SMA fixing member 155, biasspring 131, drive arm 121 and displacement input section 123. Theimaging optical system 201 is fixed inside the lens barrel 111. Theimage pickup device 301 is arranged on the base plate 101 in thisexample, but this is not essential. It is sufficient only if it isarranged at the focus position of the imaging optical system 201.

In FIG. 2 a, the SMA 151 is formed like a wire having a diameter ofabout several tens of microns, and is extended on the two displacementinput sections 123 and the tension guide 153 mounted on the drive arm121. Both ends of the SMA 151, being stretched by a predeterminedtension, are fixed onto the SMA support member 105 by caulking or othermethod through the two SMA fixing members 155 serving also aselectrodes.

Each of two beams 131 a of the lens drive frame 113 is mounted on thetwo flat portions 121 a of the drive arm 121, and the movement of theflat portion 121 a of the drive arm 121 is transmitted to the lens driveframe 113. An annular portion 113 b of the lens drive frame 113 isbiased by the bias spring 131 from the nearest side of the paper surfaceto the furthest side in FIG. 2 a. This allows the beam 113 a of the lensdrive frame 113 to be pressed against the flat portion 121 a of thedrive arm 121.

FIG. 2 b shows the situation where electric current is not applied tothe SMA 151. The lens barrel 111 is integrally formed with the lensdrive frame 113 into one piece by adhesion or similar method. It isbiased downwardly from the top of the paper in the direction of theoptical axis 203 by the bias spring 131 as a bias member of the presentinvention, and is pressed against the base plate 101. The drive arm 121is biased downwardly from the top of the paper in the direction of theoptical axis 203 by means of two flat portions 121 a and two beams 131 aof the lens drive frame 113 by the bias spring 131.

FIG. 2 c shows the situation where the electric current is applied tothe SMA 151. The drive arm 121 has a so-called pantograph structure.When current flows into the SMA 151, the length of the SMA 151 isreduced, and this force of reduction acts on the two displacement inputsections 123 and is converted into a compression force Fx forcompressing the drive arm 121.

The compression force Fx allows the drive arm 121 to press the lensbarrel 111 and lens drive frame 113 upwardly from the bottom of thepaper in the direction of the optical axis 203 through the two flatportions 121 a and two beams 131 a against the biasing force Fz by theaforementioned bias spring 131. Thus, the imaging optical system 201 isfed out upwardly from the bottom of the paper in the direction ofoptical axis 203 namely, from the infinite side to the closest side.

As described above, the SMA 151 and bias spring 131 serves as anactuator to drive the imaging optical system 201 through the lens barrel111, lens drive frame 113 and drive arm 121. In this case, the imagingoptical system 201 is a driven member of the present invention.

The following describes the relationship between the SMA 151 and drivearm 121 with reference to FIGS. 3 a and 3 b and FIGS. 4 a, 4 b and 4 c.FIGS. 3 a and 3 b are schematic diagrams showing the relationshipbetween the SMA 151 and drive arm 121. FIG. 3 a represents the operationof the SMA 151, and FIG. 3 b shows the operation of the drive arm 121.

In FIG. 3 a, assume that the SMA 151 contracts in length from length Ls1to length Ls2. Both ends of the SMA 151 fixed onto the SMA fixingmembers 155 and the center hitched by the tension guide 153 cannot bemoved. Thus, a change in the length of the SMA 151 makes the positionalchange X in the position of the portions 151 a and 151 b wherein the SMA151 is kept in contact with the displacement input section 123 of thedrive arm 121. The positional change X allows the aforementionedcompression force Fx to be applied to the displacement input section123.

In FIG. 3 b, in response to the compression force Fx, each of the twodisplacement input sections 123 of the drive arm 121 is pushed inwardlyin the pantograph shape by “X”. Then the drive arm 121 is deformed, andthe flat portions 121 a of the drive arm 121 are pushed upwardly by themoving distance Z from the bottom of the paper in FIG. 3 b against thebiasing force Fz of the bias spring 131.

FIGS. 4 a, 4 b and 4 c are the charts representing the relationshipbetween the moving distance Z of the aforementioned drive arm 121—i.e.,the feed-out distance Z of the imaging optical system 201—and thecharacteristics of the SMA 151. FIG. 4 a shows the relationship betweenthe feed-out distance Z and length Lsma of the SMA 151. FIG. 4 b showsthe relationship between the length Lsma of the SMA 151 and theresistance Rsma. FIG. 4 c shows the relationship between the feed-outdistance Z and the resistance Rsma of the SMA 151.

In FIG. 4 a, the relationship between the moving distance Z of theaforementioned drive arm 121—i.e., the feed-out distance Z of theimaging optical system 201—and the characteristics of the SMA 151 can beexpressed as a 1-to-1 relationship although it is nonlinear, withoutdepending on the ambient temperature Ta of the SMA 151. Assume that thelength of the SMA 151 is Lsma=L0 when drive current is not applied tothe SMA 151, and the feed-out distance Z=Z0 in this case. When the drivecurrent is applied to the SMA 151, and heat is generated by the SMA 151,the length Lsma of the SMA 151 is reduced, and, as shown in FIGS. 3 aand 3 b, the compression force Fx of the SMA 151 is generated to pushthe drive arm 121 upward. However, since the biasing force Fz of thebias spring 131 is greater until the SMA length Lsma becomes to be Lhp,the feed-out distance Z remains unchanged being z0.

When the drive current is further increased so that the SMA 151 lengthLsma is equal to or less than Lhp, the compression force Fx of the SMA151 is increased to be greater than the biasing force Fz of the biasspring 131. Thus, the drive arm 121 is pushed upwardly. Assume thefeed-out distance Z is Zinf for focusing the imaging optical system 201at infinity, and SMA 151 length Lsma is Linf at this time. Also assumethe feed-out distance Z is Znt for focusing the imaging optical system201 at the closest distance, and the SMA 151 length Lsma is Lnt at thistime. The area where the feed-out distance Z is from Z0 to Zinfcorresponds to the area where focusing cannot be achieved by the imagingoptical system 201 (hereinafter referred to as “over-infinity area”).

In FIG. 4 b, assume the SMA 151 resistance Rsma is R0 when the drivecurrent is not applied to the SMA 151, namely, when SMA 151 lengthLsma=L0. When the drive current is applied to the SMA 151, the SMA 151generates heat using the Joule heat resulting from the resistance Rsmaof the SMA 151. Thus, the SMA 151 temperature Tsma is raised. In thecase where the SMA 151 is independent, when SMA 151 temperature Tsma israised and when the SMA 151 length Lsma has started to be reduced, theSMA 151 resistance Rsma increases at first. When the length has beenreduced below a predetermined level, the SMA 151 resistance Rsma startsto reduce.

However, in the system such as in the AF mechanism 100 wherein thebiasing force Fz is always applied to the SMA 151 by the bias spring131, the aforementioned turnover of the change in resistance is hardlyobserved. A 1-to-1 relationship (although this is nonlinear) is known tobe held between the SMA 151 length Lsma and the resistance Rsma, withoutdepending on the ambient temperature Ta of the SMA 151.

It is assumed that the SMA 151 resistance Rsma is Rhp when SMA 151length Lsma is Lhp. Similarly, it is assumed that the resistance Rsma isRinf when SMA 151 length Lsma is Linf for focusing the imaging opticalsystem 201 at infinity. It is also assumed that the resistance Rsma isRnt when SMA 151 length Lnt for focusing the imaging optical system 201at the closest distance.

In FIG. 4 c, from the relationship discussed with reference to FIG. 4 aand FIG. 4 b, a 1-to-1 relationship (although this is nonlinear) is heldbetween the feed-out distance Z of the imaging optical system 201 andthe resistance Rsma of the SMA 151, without depending on the ambienttemperature Ta of the SMA 151. When the electric current is applied tothe SMA 151, and heat is generated, the resistance Rsma of the SMA 151is reduced, and the length Lsma is also reduced, while the feed-outdistance Z is increased. To be more specific, the imaging optical system201 is fed out from the infinity side to the closest side. While theresistance Rsma of the SMA 151 is in the range of R0 to Rhp, the biasingforce Fz of the bias spring is greater than compression force Fx of theSMA 151. Thus, the feed-out distance Z remains unchanged being z0.

While the SMA 151 resistance Rsma is Rhp through Rinf, the imagingoptical system 201 is located in the over-infinity area wherein focusingis disabled. The focusing of the imaging optical system 201 is enabledwhile Rsma is Rinf through Rnt. The area where Rsma is less than Rntcorresponds to the area wherein focusing is achieved at a position stillcloser than the closest distance. In this area, sufficient opticalproperties cannot usually be obtained due to the aberration of theimaging optical system 201 and a matter of peripheral light.

As shown in FIG. 4 c, a 1-to-1 relationship (although not linear) isheld between the moving distance of the drive arm 121, i.e., thefeed-out distance Z of the imaging optical system 201 and resistanceRsma of the SMA 151, without depending on the ambient temperature Ta ofthe SMA 151. To be more specific, if control is provided so that theresistance of the SMA 151 will be equal to a predetermined resistance,the focused position of the imaging optical system 201 can becontrolled, without depending on the ambient temperature Ta of the SMA151.

FIGS. 5 a and 5 b show the relationship between the feed-out distance Zof the imaging optical system 201 and the target resistance Rsma of theSMA 151. FIG. 5 a is an enlarged view of a part of the range where Rsmais from Rinf to Rnt in the chart representing the relationship betweenthe feed-out distance Z and target resistance Rsma in FIG. 4 c. FIG. 5 bshows an example of the Feed-out Position Table ZT showing therelationship of FIG. 5 a.

In the present first embodiment, focusing operation of the imagingoptical system 201 is assumed to be performed by the so-called stepdrive method wherein the imaging optical system 201 is fed out byequally spaced intervals. In this case, an AF step number n (where “n”is 0(zero) or positive integer) is introduced as the parameter showingthe feed-out position of the imaging optical system 201 in the stepdrive mode. The feed-out position of the imaging optical system 201corresponding to the AF step number n is assumed as Z(n), and Rtg(n) isassumed as the target resistance to control the resistance Rsma of theSMA 151 when the imaging optical system 201 is to be driven to thefeed-out position Z(n).

The relationship between the feed-out distance Z in FIG. 4 c and theaforementioned feed-out position Z(n) can be rearranged as follows: Thefeed-out position Z(0) at AF step number n=0(zero) corresponds to theinitial position Z0 wherein electric current is not applied to the SMA151. Similarly, the feed-out position Z(1) with AF step number n of 1 isthe infinite position Zinf for focusing the imaging optical system 201at the infinity. The feed-out position Z(nt) with AF step number n of ntis the closest position Znt for focusing the imaging optical system 201at the closest distance.

In FIG. 5 a, when imaging optical system 201 is assumed to beequidistantly fed out by an increments ΔZ, for example, positions Z(n)of imaging optical system 201 at AF step number n=k−2, k−1, k and k+1are assumed as Z(k−2), Z(k−1), Z(k) and Z(k+1). In this case, the drivecurrent Is(n) is applied to the SMA 151 to raise the temperature Tsma ofthe SMA 151, whereby, when the imaging optical system 201 is fed out,each of the target resistances Rtg(n) of the SMA 151 corresponding toeach feed-out position Z(n) of the imaging optical system 201 isRtg(k−2), Rtg(k−1), Rtg(k) and Rtg(k+1). Thus, a non-linear 1-to-1relationship is held, without depending on the ambient temperature Ta ofthe SMA 151, as described with reference to FIG. 4 c.

In FIG. 5 b, the feed-out position Table ZT includes an AF step numbern; a target resistance Rtg(n) of the SMA 151 for moving thecorresponding imaging optical system 201 to each feed-out position Z(n);and a reference SMA drive current value Is(n) for forming the resistanceRs(n) of the SMA 151 into the target resistance Rtg(n).

n=1, namely, when the target resistance Rtg(1) for focusing the imagingoptical system at the infinity is Rinf, the SMA drive current valueIs(1) is Iinf, and when the target resistance Rtg(nt) for focusing theimaging optical system at the closest distance is Rnt, the SMA drivecurrent value Is(nt) is Int. Similarly, n=k, namely, the targetresistance is Rtg(k) for focusing the imaging optical system at thefeed-out position z(k), the SMA drive current value is Is(k).

It should be noted, however, that the imaging optical system 201 have adepth of field depending on the focal distance and aperture value. Forexample, the infinite position Zinf may be set at the position which isnearer from the infinite position by the depth of field, and theresistance Rinf may be set smaller by the amount corresponding to thedepth of field. Similarly, the closest position Znt may be set fartherby the depth of field, and the resistance Rnt may be set higher by theamount corresponding to the depth of field.

The feed-out position Table ZT is prepared by a procedure where thetarget resistance Rtg(n) calculated at the time of adjusting the focusof the imaging optical system 201 and the SMA drive current value Is(n)supplied at that time are stored, for example. The feed-out positionTable ZT is provided, for example, in the storage section 340 of FIG. 1,and is used in the flow chart of FIGS. 11 and 15.

However, the aforementioned feed-out position Table ZT is not restrictedto it, and the table ZT may be made up of the target resistance Rs(n)and the approximate SMA drive voltage value Vs(n) for making theresistance of the SMA be that target resistance Rs(n).

The following describes the method of detecting the resistance Rs(n) ofthe aforementioned SMA 151 with reference to FIG. 6. FIG. 6 is a blockdiagram showing an example of the circuit structure of the SMA drivingsection 330.

In FIG. 6, the SMA driving section 330 is made of a drive section 331,SMA resistance calculating section 333, comparator section 335, driveamount calculating section 337, reference resistor 339 and others. Theoperation of the SMA driving section 330 is controlled by the controlsection 310.

To start with, the value of the reference SMA drive current Is(n) storedin the feed-out position Table ZT of FIG. 5 b in the storage section 340is transmitted to the drive section 331 through the control section 310,and the SMA drive current Is(n) is applied to the SMA 151 by the drivesection 331 through the reference resistor 339. As described above,instead of Is(n), the approximate SMA drive voltage value Vs(n) can beused to control the drive voltage.

The potentials Vd and Vsma at each side of the reference resistor 339are inputted into the SMA resistance calculating section 333, and thepresent resistance Rs(n) of the SMA 151 is calculated from thepotentials Vd and Vsma by the Formula 1 (to be described later).

The present resistance Rs(n) calculated by the SMA resistancecalculating section 333 is inputted into one of the input terminals ofthe comparator section 335, and the target resistance Rtg(n) stored inthe feed-out position Table ZT of FIG. 5 b is inputted into the otherterminal through the control section 310, whereby both of them arecompared with each other. The comparison result by the comparatorsection 335 is inputted into the drive amount calculating section 337.The drive amount of the SMA 151 (the control value of the drive currentIs(n) of drive section 331 in this example) is calculated from thecurrent resistance Rs(n) of the SMA 151 and target resistance Rtg(n) andthe result is fed back to the drive section 331.

The present resistance Rs(n) of the SMA 151 is obtained as follows: Inthe first place, assume that the resistance of the reference resistor339 is Rd. Then the potential difference (Vd−Vsma) across the referenceresistor 339 is:

Vd−Vsma=Is(n)×Rd

From this equation, the present SMA drive current Is(n) is:

Is(n)=(Vd−Vsma)/Rd

Further, the potential on the bottom end of the reference resistor 339,i.e., the potential Vsma on the top end of the SMA 151 is:

Vsma=Is(n)×Rs(n)

Thus, the current resistance Rs(n) of the SMA 151 is calculated from theabove equations:

Rs(n)=Vsma/Is(n)=(Vsma/(Vd−Vsma))×Rd  Formula 1

Since the resistance Rd of the reference resistor 339 is known, thecurrent resistance Rs(n) of the SMA 151 can be obtained by measuring thepotential Vd across the reference resistor 339, and the Vsma.

The following describes the operation of the image pickup apparatus 10as a first embodiment with reference to FIGS. 7 through 17. FIG. 7 is adiagram representing the main routine of the flow chart showing theimage pickup apparatus 10.

In FIG. 7, when the user has performed the operation, for example, ofsetting the mobile phone to the camera mode in Step S101, the power ofthe image pickup apparatus 10 is turned on in Step S103, and Step S200“status detection subroutine” is executed so that the status of the SMA151 is verified to see whether or not there is any failure including aline breakage or short circuit of the SMA 151, and to check the ambienttemperature Ta in the vicinity of the SMA 151 (status detection step).Step S200 “status detection subroutine” will be described later withreference to FIG. 8.

Then, Step S300 “lens infinite position setting subroutine” is executedand the imaging optical system 201 is set at the infinite position (lensinfinite position setting step). In Step S111, the image pickupoperation is started by the image pickup apparatus 10, and the displaysection 999 starts to display the preview image (preview step). Thepreview image displayed at the time is focused at infinity. Step S300“lens infinite position setting subroutine” will be described later withreference to FIG. 11.

In Step S113, it is checked whether the release switch is turned on bythe user or not. The system waits at Step S113 until the release switchis turned on (release detection step). When the release switch is turnedon (Step S113: Yes), Step S400 “AF subroutine” is executed, and theimaging optical system 201 moves to the focused position of the subject(AF process). Step S400 “AF subroutine” will be described later withreference to FIG. 12.

The image pickup operation is performed in Step S121 (image pickupstep). The captured image data is stored in the storage section 340(image data storing step), and the captured image is displayed on thedisplay section 999 in Step S123 when required (image display step). InStep S125, verification is made to determine if the image pickupoperation is to be terminated or not (image pickup termination checkprocess). If the imaging operation is not terminated (Step S125: No),the system goes back to Step S200 “status detection subroutine” whereinthe status of the SMA 151 is checked. After that, the aforementionedoperation is repeated.

Upon termination of the image pickup operation (Step S125: Yes), thepower source of the image pickup apparatus 10 is turned off in StepS131, and a series of operations is terminated. The aforementionedoperations of the image pickup apparatus 10 are controlled by thecontrol section 310.

FIG. 8 is a flow chart showing Step S200 “status detection subroutine”of FIG. 7;

As shown in FIG. 8, in Step S201, the AF step number n indicating thefeed-out position of the imaging optical system 201 is set to “0 (zero)”indicating the initial position (the initial position parameter settingup step). In Step S203, a predetermined initial current Is(0) stored inthe storage section 340 is applied to the SMA 151 (initial currentapplication step). The initial current Is(0) is about severalmilliamperes, for example. When the initial current Is(0) is applied,the temperature Tsma of the SMA 151 gets higher than the ambienttemperature Ta of the SMA 151, for example, the focus adjustment deviceof the imaging optical system 201 is provided with a function ofdetecting the increment ΔTsma of the temperature Tsma of the SMA 151,and the increment ΔTsma of the temperature Tsma at the time of adjustingthe focus is stored in the storage section 340. Then correction can bemade by the amount of ΔTsma.

In Step S205, the initial resistance Rs(0) of the SMA 151 is detected bythe SMA resistance calculating section 333 using the aforementionedFormula 1 (initial resistance calculation step), wherein the resistanceRs(0) of the SMA 151 when drive current is not applied to the SMA 151 ofFIGS. 4 a, 4 b and 4 c is R0. It should be noted, however, that the timeduration when a predetermined initial current Is(0) is applied can bethe same as the time duration required to detect the initial resistanceRs(0) of the SMA 151 in Step S205.

Although details are described later with reference to FIG. 10 a, itshould be pointed out that, when drive current Is(n) is not applied tothe SMA 151, the initial resistance Rs(0) has a one-to-one relation withthe ambient temperature Ta of the SMA 151. Thus, the initial resistanceRs(0) of the SMA 151 having been detected by application of the initialcurrent Is(0) can be considered to correspond to the sum of the ambienttemperature Ta of the SMA 151 and the temperature increment ΔTsmaresulting from initial current Is(0).

This is followed by the execution of Step S600 “SMA line breakagedetecting sub-routine” to check whether or not there is any failure suchas a line breakage or short circuit of the SMA 151 (SMA line breakagedetecting step). Step S600 “SMA line breakage detecting sub-routine”will be described later with reference to FIG. 9. If the status of theSMA 151 is normal, the ambient temperature Ta is read out of the ambienttemperature Table TaT (to be described later with reference to FIG. 10b) in Step S207 by the control section 310 based on the resistance Rs(0)of the SMA 151 detected in the Step S205. Alternatively, the ambienttemperature Ta is calculated from the ambient temperature Table TaT(ambient temperature calculating step).

In Step S209, the temperature increase ΔTsma due to the initial currentIs(0) stored in the storage section 340 is subtracted by the controlsection 310 from the ambient temperature Ta having been read out of theambient temperature Table TaT in Step S207 or having been calculated(ambient temperature correction step). This procedure offsets thetemperature increase due to the initial current Is(0), and the trueambient temperature Ta can be obtained. Then the system goes back toStep S200 of FIG. 7.

Alternatively, in Step S203, initial current Is(0) is reduced to such asmall current that heat is hardly generated by the SMA 151 per se,whereby the temperature Tsma of the SMA 151 agrees with the ambienttemperature Ta of the SMA 151. This procedure, if taken, will eliminatethe need of offsetting the temperature increase ΔTsma due to the initialcurrent Is(0), and hence will eliminate the use of the Step S209.

In this case, since the initial current Is(0) is very small, thepotentials Vd and Vsma at each side of the reference resistor are verysmall. Thus, in order to improve the detection accuracy, a measure ispreferably taken to increase the detection gain or the like of the SMAresistance calculating section 333. In this case, the control section310 serves as a status detection section, line breakage detectionsection, temperature detection section and temperature correctionsection in the present invention. Further, the Is(0) may be a currentwith which the SMA keeps a martensite phase without transiting into anaustenite phase.

It should be noted that detection of the ambient temperature Ta by StepS200 “status detection subroutine” is used to correct the temperaturecharacteristics of the image pickup apparatus 10 and is preferablyexecuted at every image pickup operation. However, if there is not a bigchange in ambient temperatures among imaging operations in the mode ofcontinuously capturing a plurality of images, the ambient temperature Tashould be detected immediately before the first imaging operation.

FIG. 9 is a flow chart showing Step S600 “SMA line breakage detectingsub-routine” of FIG. 8. In this case, prior to the calculation of theambient temperature Ta in Step S207 of FIG. 8, a measure is taken tocheck a trouble with the resistance resulting from the wire breakage orshort circuit of the SMA 151.

In FIG. 9, verification is made in Step S601 to see whether or not theinitial resistance Rs(0) of the SMA 151 detected in Step S205 of FIG. 8is smaller than a predetermined resistance R1. If the initial resistanceRs(0) of the SMA 151 is equal to or greater than a predeterminedresistance R1 (Step S601: No), the SMA 151 is determined to have beendisconnected. Then an SMA disconnection flag is set in Step S651, andapplication of current to the SMA 151 is disabled, for example. Thesystem goes to the “trouble processing routing” wherein a troublehandling process is taken, for example, by giving a visual display tonotify the abnormal status or issuing an alarm sound. The details of the“trouble processing routing” will be described later.

When the initial resistance Rs(0) of the SMA 151 is smaller than apredetermined resistance R1 (Step S601: Yes), verification is made inStep S611 to check whether or not the initial resistance Rs(0) of theSMA 151 is greater than a predetermined resistance R2. When the initialresistance Rs(0) of the SMA 151 is equal to or smaller than apredetermined resistance R2 (Step S611: No), the SMA 151 is determinedto have been short circuited or to be suffering from much currentleakage, and an AF disable flag is set in Step S631. The system thengoes to the “lens position fixing routine” wherein the imaging opticalsystem 201 is moved to a predetermined fixed position (e.g., the regularfocus position for focusing at a distance of several meters), forexample, by other mechanical means. The details of the “lens positionfixing routine” will not be described.

When the initial resistance Rs(0) of the SMA 151 is greater than apredetermined resistance R2 (Step S611: Yes), an SMA normal flag is setin Step S621, and the system goes to the Step S600 of FIG. 8.

The aforementioned predetermined resistances R1 and R2 are a resistancewhich is slightly greater than the range of resistance that can be takenby the SMA 151, and a resistance which is slightly smaller than therange of resistance that can be taken by the SMA 151, respectively. Forexample, if the resistance that can be taken by the SMA 151 is in therange of 30 through 35Ω, then R1=50Ω, and R2=20Ω.

FIGS. 10 a and 10 b show the relationship between the initial resistanceRs(0) of the SMA 151 and the ambient temperature Ta of the SMA 151. FIG.10 a is a chart representing the relationship between the initialresistance Rs(0) and ambient temperature Ta. FIG. 10 b shows an exampleof the ambient temperature Table TaT.

When electric current is not applied to the SMA 151, the initial lengthLs(0) and initial resistance Rs(0) retain the one-to-one relationship asshown in FIG. 4 b, and the relationship is known to be changed by theambient temperature Ta of the SMA 151. Thus, the one-to-one relationalso is held between the ambient temperature Ta and initial resistanceRs(0). FIG. 10 a shows an example of this relationship. Here therelationship between the ambient temperature Ta and initial resistanceRs(0), wherein the ambient temperature Ta is plotted on the horizontalaxis, with the initial resistance Rs(0) plotted on the vertical axis.

The initial resistance Rs(0) (30Ω in this example) at the maximum value(+60° C. in this example) of the ambient temperature Ta should be set ata level higher than the infinite position resistance Rinf correspondingto the infinite position of the imaging optical system 201. If thisrelationship is reversed, the imaging optical system 201 will pass bythe infinite position Zinf and will go to the position wherein focusingis achieved at an finite distance, without the SMA drive current Is(n)being applied to the SMA 151 in the vicinity of the maximum value of theambient temperature Ta. This explains the reason why the over-infinityarea is provided in the first embodiment.

In FIG. 10 b, the ambient temperature Table TaT is a tabulated versionrepresenting the relationship given in the form of a chart in FIG. 10 a.This Table is a conversion table made up of the initial resistance Rs(0)of the SMA 151 and the ambient temperature Ta of the SMA 151corresponding to Rs(0). In this example, the range from −20° C. through+60° C. which is the guaranteed operation temperature range of the imagepickup apparatus 10 is assumed as the range of the Table, and theinitial resistance Rs(0) within this range is divided at an equallyspaced intervals (e.g., the range from 35Ω to 30Ω at an interval of 1Ω).The ambient temperature Ta corresponding to each initial resistanceRs(0) is organized in the form of a table. The interval of dividing theTable is determined with consideration given to the required detectionaccuracy of the ambient temperature Ta.

Alternatively, when the initial resistance Rs(0) not present in theambient temperature Table TaT has been detected in Step S205 of FIG. 8,the ambient temperature Ta of the SMA 151 can be calculated in Step S207of FIG. 8, for example, by proportional distribution from the initialresistance Rs(0), on the table, above and below the initial resistanceRs(0) which has been detected. Further, it is also possible to store theconversion formula for converting the initial resistance Rs(0) into theambient temperature Ta, instead of the ambient temperature Table TaT.

In FIG. 11, the AF step number n denoting the feed-out position of theimaging optical system 201 is set to “1” denoting the infinite position(infinite position parameter setting up process) in Step S301. In StepS303, the infinite position resistance Rinf of the SMA 151 correspondingto feed-out position Z(1)=Zinf at the time of the imaging optical system201 being focused at infinity, and the approximate SMA drive currentvalue Iinf for the resistance of the SMA 151 to be the infinite positionresistance Rinf are read out from the feed-out position Table ZT of FIG.5 b (infinite position resistance read-in process).

In Step S305, the target resistance Rtg(n) used as a control target inthe following control procedure is set to the infinite positionresistance Rinf having been read in Steps S303 (infinite position targetresistance setup process). In Step S307, the drive current Is (n) of theSMA 151 is set to the reference SMA drive current value Iinf having beenread in Step S303 (infinite position drive current value setup process).

Then, the Step S500 “lens drive subroutine” is executed, and the drivecurrent Is(n) applied to the SMA 151 is controlled in such a way thatthe resistance Rs(n) of the SMA 151 is becomes the infinite positionresistance Rinf, whereby the imaging optical system 201 is moved to theinfinite position Zinf (imaging optical system infinite position settingup step). Then, the system goes to Step S300 of FIG. 7. Step S500 “lensdrive subroutine” will be described with reference to FIG. 12.

FIG. 12 is a flow chart showing Step S500 “lens drive subroutine” ofFIGS. 11 and 15 (to be described later).

In FIG. 12, the settling time tst(n) is read out of the settling timeTable STT (settling time reading process) based on the AF step number ndenoting the feed-out position of the imaging optical system 201 and theambient temperature Ta of the SMA 151 in Step S501. The ambienttemperature Ta can be accurately detected when the initial resistanceRs(0) of the SMA 151 is detected by the Step S200 “status detectionsubroutine” of FIG. 7.

As described above, the settling time tst(n) indicates the time requiredfor the feed-out position Z(n) of the imaging optical system 201 to besettled when the imaging optical system 201 has been moved from the AFstep number n−1 to the AF step number n. The settling time tst(n) andsettling time Table STT will be described later with reference to FIGS.13 a, 13 b and FIG. 14.

The settling time tst(n) read out at Steps S501 on timer TM(n) is set atStep S503. A predetermined time ti required to execute any one of thethree processes from Steps S507 through S551 is subtracted from thetimer TM(n) in Steps S505.

In Step S507, the SMA 151 generates heat (drive current applicationstep) when drive current Is(n) is applied to the SMA 151. In Step S509,the resistance Rs(n) of the SMA 151 is detected by the circuit of theaforementioned FIG. 6 according to the Formula 1 (resistance detectionstep). In Step S511, verification is made to see whether or not theresistance Rs(n) of the SMA 151 detected in Step S509 is equal to orgreater than the value (Rtg(n)-Rp) which is smaller than the targetresistance Rtg(n) by the allowable error Rp.

If the resistance Rs(n) of the SMA 151 is equal to or greater than thevalue (Rtg(n)-Rp) (Step S511: Yes), verification is made in Step S513 tosee whether or not the resistance Rs(n) of the SMA 151 is equal to orsmaller than the value (Rtg(n)+Rp) which is greater than the targetresistance Rtg(n) by the allowable error Rp. If the resistance Rs(n) isequal to or smaller, i.e., if the resistance Rs(n) of the SMA 151 iswithin the range of the target resistance Rtg(n) allowable error Rp(Step S513: Yes), the resistance Rs(n) of the SMA 151 is regarded ashaving reached the target value, and the value of the drive currentIs(n) of the SMA 151 is fixed in Step S521. Then the system goes to StepS551.

If the resistance Rs(n) of the SMA 151 is greater than the value(Rtg(n)+Rp) which is greater than the target resistance Rtg(n) byallowable error Rp (Step S513: No), the temperature of the SMA 151 isregarded as being excessively low in Step S513, and the temperature ofthe SMA 151 is raised in Step S531. Thus, the drive current Is(n) of theSMA 151 is set to a level which is greater than the present value by apredetermined value Ist, and the system goes to the Step S551.

If the resistance Rs(n) of the SMA 151 is smaller than the value(Rtg(n)-Rp) which is smaller than the target resistance Rtg(n) by theallowable error Rp (Step S511: No), the temperature of the SMA 151 isregarded as being excessively high, and the temperature of the SMA 151is reduced in Step S541. Thus, the drive current Is(n) of the SMA 151 isset to a level which is smaller than the present value by thepredetermined value Ist, and the system goes to the Step S551.

In Step S551, verification is made to see whether or not the timer TM80)is equal or less than 0, in other words, the settling time tst(n) haselapsed after the timer TM(n) was set in Steps S503. If the settlingtime tst(n) has elapsed (Step S551: Yes), the system returns to theupper level routine of FIG. 11 and FIG. 15.

If the settling time tst(n) has not elapsed (Step S551: No), the systemgoes back to Step S505, and the operations of Step S505 through StepS551 are repeated until the settling time tst(n) elapses.

Here, Steps S511 and S513 are a resistance evaluation step, and the StepS531 and S541 are a drive current feedback step.

Step S531 and S541 show method wherein the drive current Is(n) of theSMA 151 is increased or decreased in a step manner by the predeterminedvalue Ist. It is also possible to make such an arrangement that, basedon the result of comparison in the comparator section 335 of FIG. 6between the present resistance Rs(n) of the SMA and the targetresistance Rtg(n), a new value of the drive current Is(n) of the SMA 151is calculated by the drive amount calculating section 337, and the drivecurrent Is(n) of the SMA 151 is controlled based on the result of thecalculation.

FIGS. 13 a and 13 b are schematic diagrams showing the aforementionedsettling time tst(n). FIG. 13 a, which is different from the methoddescribed with reference to FIG. 12, shows the drive waveform and movingwaveform of the imaging optical system 201 when the imaging opticalsystem 201 is fed out by the step drive at the same intervals. FIG. 13 bshows the comparison between the time required for performing the stepdrive at a predetermined intervals, and the time required for performingthe step drive while waiting for the lapse of the settling time asdescribed in FIG. 12.

In FIG. 13 a, when the drive waveform DP is applied to the imagingoptical system 201, and the imaging optical system 201 is moved from theposition Z(k−2) of AF step number n=k−2 to the position Z(k−1) of AFstep number n=k−1, the imaging optical system 201 actually moves in themanner similar to the moving waveform MW due to mechanical responsedelay, bounding and other factors. Assume that the settling time tst(n)is from the stat or the drive to the timing when the response delay,bounding and other factors have converged, and the position of theimaging optical system 201 is settled. The settling time tst(n) changesaccording to the present position Z(n) of the imaging optical system201, ambient temperature Ta and other factors. Thus, when the step driveis performed at a predetermined intervals Δt, with consideration givento various conditions, the predetermined interval Δt must be set at alevel equal to or greater than the longest settling time plus the timets421 required for executing Step S421 “AF data acquisition step” ofFIG. 15. A lot of time is required to move the imaging optical system201 to the focused position.

As compared to the case wherein the aforementioned step drive isperformed at a predetermined intervals Δt (drive waveform DP denoted bysolid line in the drawing) in FIG. 13 b, Step S400 “AF subroutine” ofFIG. 7 is executed after the lapse of the settling time tst(n) at eachstep in the step drive of the imaging optical system 201, as shown inFIG. 12. Then, the next step drive is performed (drive waveform DPstindicated by the one-dot chain line in hte4 drawing) immediately afterS400. This procedure makes it possible to reduce the time, for example,by time tsh for driving the imaging optical system 201 from the positionZ(k−2) of the AF step number n=k−2 to the position Z(k+1) of the AF stepnumber n=k+1.

FIG. 14 is a diagram showing an example of the stability time table STT.As described with reference to FIGS. 13 a and 13 b, the settling timetst(n) varies with the current position Z(n) of the imaging opticalsystem 201, ambient temperature Ta and other factors. Thus, the settlingtime Table STT is made up of the AF step number n and the settling timetst(n) at that position for each ambient temperature Ta.

In this example, similarly to the case of FIGS. 10 a and 10 b, the rangeof the Table can be set to the range from −20° C. to +60° C. which isthe guaranteed operation temperature range of the image pickup apparatus10, for example. The ambient temperature Ta for this range is divided atan equally spaced intervals (e.g., in increment of 10° C.), and the AFstep number n and the settling time tst(n) corresponding to the AF stepnumber n are incorporated in the Table for each ambient temperature Ta.The width for dividing the ambient temperature Ta can be determined withconsideration given to the accuracy required of the settling timetst(n).

If the ambient temperature Ta is not included in the settling time TableSTT, the settling time tst(n) can be calculated by proportionaldistribution from the settling time Table STT. It is also possible touse the settling time Table STT of the closest ambient temperature Ta.The settling time Table STT is used with reference to FIG. 12.

FIG. 15 is a flow chart showing the Steps S400 “AF subroutine” of FIG.7. The AF operation performed by this sub-routine uses the so-called themountain climbing control method, without requiring installation of aseparate sensor designed specifically for AF operations. The mountainclimbing control method refers to the technique of detecting thecontrast of the image and finding out the position of the maximumcontrast, i.e., the focused position, while moving the imaging opticalsystem 201 in a step manner at equally spaced intervals from theinfinity side to the closest side.

The focus information of FIG. 1—i.e., the AF data AFD(n) denoting thecontrast of the image in this case—can be defined normally as the sum ofthe differences between the image data of the adjacent AF pixels withinthe AF area on the image pickup device 301. Needless to say, it is alsopossible to use other methods including the sum of the differencesbetween the image data of all the pixels of the image pickup device 301.

In FIG. 15, the Step S300 “lens infinite position setting subroutine” ofFIG. 11 is executed in Step S401, and the imaging optical system 201 isset to the infinite position (AF step number n=1). Under this condition,the AF data AFD(1) at the infinite position is acquired (infinity AFdata acquisition step).

In Step S411, “1” is added to the AF step number n (parameter changestep). In Step S413, the target resistance Rtg(n) corresponding to theAF step number n and the reference SMA drive current value Is(n) areread out from the feed-out position Table ZT described with reference toFIG. 5 b, based on the AF step number n (target resistance read-outprocess). This is followed by execution of the Step S500 “lens drivesubroutine” of FIG. 12, with the result that the imaging optical system201 is fed out from the infinity side toward the closest side by onestep (imaging optical system feed-out step).

In Step S413, the target resistance Rtg(n) and the approximate SMA drivecurrent value Is(n) were assumed to be read out from the feed-outposition Table ZT. However, it is also possible to make sucharrangements that, in response to the difference between the currentresistance Rs(n) of the SMA and target resistance Rtg(n) in thecomparator section 335 of FIG. 6, the change value of the drive currentIs(n) of the SMA 151 is calculated by the drive amount calculatingsection 337 in the Step S500 “lens drive subroutine”, as described withreference to FIG. 12. Then, the drive current Is(n) of the SMA 151 iscontrolled based on the calculated change value of the drive currentIs(n).

In this case, the approximate SMA drive current value Is(n) needs not tobe read out. The feed-out position Table ZT can be made up of the AFstep number n, and the target resistance Rtg(n) of the SMA 151 when thecorresponding imaging optical system 201 is moved to each feed-outposition Z(n).

In Step S421, the AF data AFD(n) denoting the image contrast is acquired(AF data acquisition step). In Step S423, verification is made to seewhether or not the AF data AFD(n) acquired in Step S421 is smaller thanthe AF data AFD(n−1) acquired with the imaging optical system 201positioned at the one-step previous position (AF data comparisonprocess).

When the AF data AFD(n) is equal or greater than the AF data AFD(n−1)(Step S423: No), the system goes back to the Step S411, and “1” is addedto the AF step number n. After that, the imaging optical system 201 isfed out in a step manner, repeatedly acquiring the AF data AFD(n) andcomparing it with the AF data AFD(n−1), from the infinity side towardthe closest side as if it were climbing a mountain, until the AF dataAFD(n) is smaller than the AF data AFD(n−1), namely, until the imagingoptical system 201 passes by the focused position of the imaging opticalsystem 201 wherein the image contrast is maximized.

When the AF data AFD(n) is smaller than the AF data AFD(n−1) (Step S423:Yes), the imaging optical system 201 is regarded as having passed by thefocused position. At and after Step S431, operations are performed toget the imaging optical system 201 back to the focused position.

It is the common practice in the conventional AF operation that, in thecase where the imaging optical system 201 has passed by the focusedposition, the imaging optical system 201 is once fed back to the side ofthe initial position Z(0) from the focused position in order to correctthe backlash caused by the gear and cam, before the imaging opticalsystem 201 is moved to the feed-out position Z(n−1) which is supposed tobe the focused position. Moving the imaging optical system 201 in thismethod takes much time, since the imaging optical system 201 is fed outafter having been fed in.

In the first embodiment, however, the imaging optical system 201 ismoved from the feed-out position Z(n) of the imaging optical system 201to the feed-out position Z(n−1) as the focused position in oneoperation. This arrangement realizes a substantial reduction in the timeof moving the imaging optical system 201.

However, similarly to the case of the backlash in the conventional drivemechanism using the gear and cam, the AF mechanism 100 described withreference to FIGS. 2 a, 2 b and 2 c and FIGS. 4 a, 4 b and 4 c containshysteresis in the relationship between the target resistance Rtg(n) ofthe SMA 151 and the feed-out position of the imaging optical system 201Z(n) in the case wherein the imaging optical system 201 is fed out fromthe infinity side toward the closest side, as compared to the casewherein the imaging optical system 201 is fed in from the closest sidetoward the infinity side. The hysteresis will be described later withreference to FIG. 16.

Thus, even if control is provided in the Step S500 “lens drivesubroutine” of FIG. 12 so that the resistance Rs(n) of the SMA 151 isequal to the one-step previous target resistance Rtg(n−1) of the SMA151, the imaging optical system 201 cannot be fed back to the focusedposition.

In Step S431, the resistance correction value Rcor(n−1) and currentcorrection value Icor(n−1) are read out from the hysteresis correctiontable HCT (to be described later with reference to FIG. 17) (hysteresiscorrection value read-out step), based on the one-step previous targetresistance Rtg(n−1) of the SMA 151, and the ambient temperature Ta ofthe SMA 151. The initial resistance Rs(0) of the SMA 151 is detected inStep S200 “status detection subroutine” of FIG. 7, whereby the ambienttemperature Ta is detected at a high precision. In this case, theresistance correction value Rcor(n−1) is the hysteresis correction valuein the present invention.

In Step S433, the target resistance Rtg(n) of the SMA 151 is set toRs(n−1)+Rcor(n−1) (target resistance correction process). In Step S435,the drive current Is(n) of the SMA 151 is set to =Is(n−1)−Icor(n−1)(drive current correction process). This is followed by the execution ofStep S500 “lens drive subroutine” of FIG. 12. With consideration givento the hysteresis, the imaging optical system 201 is fed back to thefocused position in one operation (imaging optical system feed-inprocess), and the system returns to the upper level routine of FIG. 7.

In this case, resistance correction value Rcor(n−1) and currentcorrection value Icor(n−1) are read out from the hysteresis correctiontable HCT in Step S431. In Step S433, the target resistance Rtg(n) ofthe SMA 151 is corrected to be Rs(n−1)+Rcor(n−1). In Step S435, thedrive current Is(n) of the SMA 151 is corrected to be Is(n−1)−ICor(n−1).

As described with reference to FIG. 12, however, in Step S500 “lensdrive subroutine”, the change value of the drive current Is(n) of theSMA 151 can be calculated in the drive amount calculating section 337 inresponse to the difference between the current resistance Rs(n) of theSMA and the target resistance Rtg(n) in the comparator section 335 ofFIG. 6, and the drive current Is(n) of the SMA 151 can be controlled,based on the change value of the drive current Is(n) having beencalculated.

In this case, only the resistance correction value Rcor(n−1) is needed.There is no need of reading out the current correction value Icor(n−1).The hysteresis correction table HCT (to be described later) can be madeup of the AF step number n at various ambient temperatures Ta correctedresistance Rcor(n−1) corresponding to the temperature Ta. Further, thereis no need of using the Step S435.

FIG. 16 is a schematic chart showing the hysteresis between the targetresistance Rtg(n) of the SMA 151 and the feed-out position Z(n) of theimaging optical system 201 when the imaging optical system 201 is fedout and fed in. It shows the relationship between the target resistanceRtg(n) of the SMA 151 as the control target in the AF operation, and theposition Z(n) of the imaging optical system 201.

In FIG. 16, in the first embodiment, the drive current Is(n) is appliedto the SMA 151 and the SMA 151 contracts by generating heat, whereby theimaging optical system 201 is fed out from the infinity side toward theclosest side. The relationship between the target resistance Rtg(n) ofthe SMA 151 and the feed-out position Z(n) of the imaging optical system201 at the time of feed-out describes the locus FW as shown in thedrawing. Here the imaging optical system 201 is moved from the positionZ(k−1) of the AF step number n=k−1 to the position Z(k) of the AF stepnumber n=k. When the AF data AFD (k) is regarded as being smaller thanthe AF data AFD(k−1) in Step S423 of FIG. 15, the imaging optical system201 must be fed from the position Z(k) into the position Z(k−1) which isthe focused position.

In this case, the relationship between the target resistance Rtg(n) ofthe SMA 151 at the time of feed-in operation of the imaging opticalsystem 201 and the position Z(n) of the imaging optical system 201describes a path BW different from that at the time of feed-out, becauseof the hysteresis mainly caused by the mechanical factors such asdistortion of the drive arm 121 shown in FIGS. 2 a, 2 b and 2 c.

Thus, to feed the imaging optical system 201 from the position Z(k) intothe position Z(k−1), the target resistance Rtg(n) of the SMA 151 must beset to a value greater by the resistance correction value Rcor(k−1) thanthe target resistance Rtg(k−1) at the time of feed-out operation of theposition Z(k−1). Accordingly, the SMA drive current value Is(n) at thattime must be set to a value smaller by the current correction valueIcor(k−1) than the SMA drive current value Is(k−1) at the time offeed-out operation. Further, the aforementioned hysteresis depends onthe coefficient of linear expansion of the components constituting theAF mechanism 100, hence on the ambient temperature Ta as well.

FIG. 17 is a schematic diagram representing an example of the hysteresiscorrection table HCT.

In FIG. 17, the hysteresis correction table HCT is a correction tablefor correcting the hysteresis when the imaging optical system 201 is fedout and fed in, as described with reference to FIG. 16. It is made up ofthe AF step number n at various ambient temperatures Ta, the resistancecorrection value Rcor(n) and current correction value Icor(n). Thehysteresis correction table HCT is stored in the storage section 340 ofFIG. 1, for example.

In this example, similarly to the case of FIGS. 10 a, 10 b and FIG. 14,the range from −20° C. through +60° C. which is the guaranteed operationtemperature range of the image pickup apparatus 10 is assumed as therange of the Table, for example. The ambient temperature Ta within thisrange is divided at equally spaced intervals (e.g., in increments of 10°C.). The AF step number n, the resistance correction value Rcor(n) andcurrent correction value Icor(n), which are corresponding to the AF stepnumber, are organized in the form of a table for each ambienttemperature Ta. The interval of dividing the ambient temperature Ta canbe determined with consideration given to the allowable error ofhysteresis. The hysteresis correction table HCT is used with referenceto FIG. 15.

As described above, in response to the difference between the currentresistance Rs(n) of the SMA and the target resistance Rtg(n) in thecomparator section 335 of FIG. 6, the change value of the drive currentIs(n) is calculated by the drive amount calculating section 337, and thedrive current Is(n) of the SMA 151 is controlled based on the changevalue of the calculated drive current Is(n). In this case, thehysteresis correction table HCT does not required the current correctionvalue Icor(n).

In the first embodiment described above, a predetermined initial currentIs(0) is applied to the SMA 151, and the initial resistance Rs(0) of theSMA 151 is detected, whereby the status of the SMA 151 including wirebreakage, short circuit and leakage can be detected. This arrangementeliminates the possibility of an abnormal operation of the image pickupapparatus 10. Further, depending on the status, even if the SMA 151 isfaulty, imaging operation can be performed, for example, by forciblysetting the imaging optical system to the pan-focus position.

A predetermined initial current Is(0) is applied to the SMA 151 todetect the initial resistance Rs(0) of the SMA 151, whereby the ambienttemperature Ta of the SMA 151 can be detected, without having to installan additional temperature sensor such as a thermistor or a temperaturedetecting circuit for detecting the temperature using the temperaturesensor. Thus, the ambient temperature Ta can be used to correct thetemperature characteristics in the AF operation of the image pickupapparatus 10 to be described later. This arrangement enhances the imagequality of the image pickup apparatus 10, and ensures cost reduction andspace saving.

According to the first embodiment described above, when the image datais displayed in the preview mode, accurate movement of the imagingoptical system 201 to the infinite position Zinf can be ensured bycontrolling the drive current Is(n) to be applied to the SMA 151 in sucha way that the resistance Rs(n) of the SMA 151 is equal to the infiniteposition resistance Rinf. This arrangement enhances the image quality ofthe image pickup apparatus 10, and ensures cost reduction and spacesaving without the need of installing an additional sensor for detectingthe feed-out position of the imaging optical system 201, or a detectingcircuit.

Further, by moving the imaging optical system 201 to the infiniteposition Zinf, a moving image can be displayed at the time of previewingwith the imaging optical system focused at infinity. This featureprovides the user with the image pickup apparatus 10 of enhancedusability for easy determination of framing for imaging. Further, thedrive current Is(n) is applied to the SMA 151 and therefore, the SMA 151is preheated. This procedure enhances the response in the drive of theimaging optical system 201 in the Step S400 “AF subroutine” to beexecuted thereafter. The user is provided with the image pickupapparatus 10 of enhanced usability.

Moreover, according to the first embodiment, in the case of step driveof the imaging optical system 201, the settling time tst(n) from theinput of the drive waveform to the completion of the movement of theimaging optical system 201 and stabilization at that position isprepared in advance in the form of a settling time Table STT. The “AFdata acquisition step” is executed immediately after the lapse of thesettling time tst(n) at each position of the step drive of the imagingoptical system 201. This is followed by execution of the immediatelynext step drive. This arrangement reduces the time of moving the imagingoptical system 201 to the focused position, as compared with theconventional method of performing the step drive at each predeterminedintervals Δt. Thus, the user is provided with the image pickup apparatus10 of enhanced usability.

According to the first embodiment described above, to correct thehysteresis when the imaging optical system 201 is fed out and fed in,the resistance correction value Rcor(n) and, if required, the currentcorrection value Icor(n) are prepared in advance in the form of thehysteresis correction table HCT for each ambient temperature Ta. Theaccurate information on the ambient temperature Ta is provided bydetecting the initial resistance Rs(0) of the SMA 151 in Step S200“status detection subroutine” of FIG. 7.

When the imaging optical system 201 is moved back to the focusedposition from the position beyond the focused position, the targetresistance Rtg(n) of the SMA 151 and, if required, the SMA drive currentvalue Is(n) are corrected using the resistance correction value Rcor(n)and current correction value Icor(n) of the hysteresis correction tableHCT. This arrangement allows the imaging optical system 201 to be movedback to the focused position from the position beyond the focusedposition in one operation. There is no need of moving the imagingoptical system 201 back to the initial position Z(0) once, as in theconventional method. Since this arrangement reduces the time of movingthe imaging optical system 201 to the focused position, the user isprovided with the image pickup apparatus 10 of enhanced usability.

The following describes a second embodiment of the present inventionwith reference to FIGS. 18 a, 18 b and FIG. 19. FIGS. 18 a and 18 b areschematic diagrams representing the shutter unit as the secondembodiment of the present invention. FIG. 18 a shows the case whereinthe shutter is closed, while FIG. 18 b shows the case wherein theshutter is fully open. In this embodiment, the shutter unit is equippedwith a coil spring-shaped SMA as a drive source of the shutter blades.

In FIGS. 18 a and 18 b, the shutter unit 400 is made up of shutterblades 401 and 402, rotary shafts 401 a and 402 a, connecting pin 403,SMA 404, bias spring 405, shutter base plate 406 and SMA drive controlsection 410. The shutter base plate 406 is equipped with a shutteraperture 406 a.

The SMA drive control section 410 serves as a drive section, shapememory alloy resistance calculating section, temperature detectionsection, storage section and temperature correction section in thepresent invention. Further, the shutter unit 400 corresponds to thedrive module of the present invention, the rotary shafts 401 a and 402a, connecting pins 403, SMA 404, shutter base plate 406 and SMA drivecontrol section 410 correspond to the drive unit of the presentinvention. The shutter blades 401 and 402 correspond to the drivenmember of the present invention.

In FIG. 18 a, the shutter blades 401 and 402 are rotatably supportedabout the rotary shafts 401 a and 402 a, respectively, and are connectedwith each other by a connecting pin 403. Between the shutter blade 401and shutter base plate 406, the SMA 404 and bias spring 405 areconnected in such a way that the forces thereof are applied in theopposite directions each other. The SMA 404 and bias spring 405 work asan actuator for driving the shutter blade 402.

When electric current is applied to the SMA 404 by the SMA drive controlsection 410, the SMA 404 contracts, the shutter blade 401 rotates aboutthe rotary shaft 401 a in the counterclockwise direction of the drawingagainst the biasing force of the bias spring 405. In synchronismtherewith, the shutter blade 402 connected by the connecting pin 403also rotates about the rotary shaft 402 a in the clockwise direction ofthe drawing. This procedure opens the shutter. Thus, the shutter hasbeen fully opened to be in the status of FIG. 18 b.

When the electric current to the SMA 404 is turned off and thecontraction of the SMA has been suspended, the shutter blade 401 isrotated about the rotary shaft 401 a by the biasing force of the biasspring 405 in the clockwise direction of the drawing. In synchronismtherewith, the shutter blade 402 connected by the connecting pin 403also rotates about the rotary shaft 402 a in the counterclockwisedirection. This procedure allows the shutter to be closed and to be inthe status of FIG. 18 a. The aforementioned operation is controlled bythe SMA drive control section 410.

FIG. 19 is a flow chart showing an example of the flow of the operationswhen the shutter unit 400 of the second embodiment is used in a digitalcamera.

In FIG. 19, when the power of the digital camera has been turned on, theambient temperature Ta is measured according to the method ofcalculating the initial resistance Rs(0) of the SMA in Step S703,similarly to the case of the Step S200 “status detection subroutine” ofFIG. 8 in the first embodiment (status detection step). The ambienttemperature Ta having been measured is used to correct the temperaturedependency of hysteresis when the subsequent operations of the shutterunit 400 are performed, for example, when the shutter blades 401 and 402are moved to the reference position immediately before opening in theStep S715 to be described later. This enhances the performance of theshutter.

This is followed by Step S705 wherein electric current is applied to theSMA 404, and the shutter blades 401 and 402 are fully opened. Then thepreview operation starts in Step S707 (preview step). In the case of thedigital camera, the AF operation is generally performed in the previewmode, differently from the case of the mobile phone in the firstembodiment. When the shutter button is pressed halfway down by the userin Step S709, and the AF switch is turned on, the AF operation andphotometric (AE) operation are performed in Step S711, and the positionof the image taking lens and exposure value are locked (AF/AE lockingstep).

In Step S713, verification is made to see whether or not the releaseswitch has been turned on with the shutter button fully pressed by theuser (release detection step). The system waits in Step S713 until therelease switch is turned on. When the release switch has been turned on(Step S713: Yes), the shutter is closed once in Step S715. In this case,however, the shutter blades 401 and 402 are moved to a pre-openingreference position where the shutter blades 401 and 402 have to beimmediately before opening (shutter blade reference position setupstep), instead of the shutter blades 401 and 402 being fed back to theinitial position by turning off of the electric current applied to theSMA 404.

Similarly to the case of the “lens infinite position set subroutine” ofFIG. 11 in the first embodiment, the shutter blades 401 and 402 isdriven to the pre-opening reference position by controlling the SMAdrive current Is(n) so that the resistance Rs(1) of the SMA is equal tothe target resistance Rtg(1) corresponding to the pre-opening referenceposition. Further, similarly to the case of the “AF subroutine” of FIG.15 in the first embodiment, the target resistance Rtg(1) of thepre-opening reference position is determined by taking into account thehysteresis between the operations of opening and closing the shutterblades 401 and 402.

In Step S717, the shutter is opened again up to the aperture valueobtained from the exposure value determined in Steps S711. In Step S719,imaging operation is performed during the time of exposure obtained fromthe exposure value determined in Steps S711. The application of electriccurrent to the SMA 404 is turned off in Step S721, and the shutterblades 401 and 402 are moved back to the initial position. In this case,Steps S717, S719 and S721 are an imaging step.

In Step S723, verification is made to see whether or not imagingoperation is terminated (imaging termination check step). If the imagingoperation is not terminated (Step S723: No), the system goes to StepS703, and the ambient temperature Ta is measured again. After that, theaforementioned operation is repeated.

If the imaging operation is terminated (Step S723: Yes), the power ofthe digital camera is turned off in Step S725, and a series ofoperations terminates.

As described above, according to the second embodiment, a predeterminedinitial current Is(0) is applied to the SMA 404 and the initialresistance Rs(0) of the SMA 404 is detected, whereby the ambienttemperature Ta of the SMA 404 can be detected, without having to installan additional temperature sensor such as a thermistor, or a temperaturedetecting circuit for detecting the temperature using the temperaturesensor. This arrangement enhances the performances of the shutter unit400, and ensures cost reduction and space saving.

Further, when the shutter is once closed in response to the user'smaking the release switch on, the drive current Is(n) of the SMA 404 iscontrolled in such a way that the resistance Rs(1) of the SMA 404 isequal to the target resistance Rtg(1) of the pre-opening referenceposition. This control ensures accurate closing of the shutter blades401 and 402 up to the pre-opening reference position without installingan additional sensor or detecting circuit for detecting the positions ofthe shutter blades 401 and 402. This arrangement decreases the releasetime lag of re-opening of the shutter in Step S717, and hence enhancesthe performances of the shutter unit 400, and ensures cost reduction andspace saving.

Further, drive current Is(n) applied to the SMA 404 preheats the SMA404. This enhances the response when re-opening the shutter in thefollowing Step S717, and provides shutter unit 400 of excellentusability.

In addition, the resistance correction value Rcor(n) is used to correctthe hysteresis of the target resistance Rtg(1) corresponding to thepre-open reference position when the shutter is opened and closed,whereby the shutter blades 401 and 402 are moved from the fully openedposition back to the pre-opening reference position in one operation.This arrangement decreases a release time lag and provides shutter unit400 of excellent usability.

Referring to FIGS. 20 a and 20 b, and FIG. 21, the following describes athird embodiment of the present invention: FIGS. 20 a and 20 b areschematic diagrams representing an image stabilization function as athird embodiment of the present invention. FIG. 20 a shows the casewherein the image stabilization function is not utilized, while FIG. 20b shows the case wherein the image stabilization function is beingutilized. In the third embodiment, an example is given to illustrate themethod of image stabilization, wherein a wire-shaped SMA is provided asa drive source, and a compensation lens incorporated in the imagingoptical system is moved to stabilize the image. However, the sameeffects can also be provided by the method of moving an image pickupelement.

In FIGS. 20 a and 20 b, the image stabilizing unit 500 is comprised of abase 510, guide rod 501, compensation lens 502, holding frame 503, SMA507, bias spring 508 and SMA drive control section 520. In this case,the SMA drive control section 520 serves as a drive section, shapememory alloy resistance calculating section, temperature detectionsection, storage section and temperature correction section in thepresent invention. The image stabilizing unit 500 corresponds to thedrive module of the present invention. The base 510, guide rod 501,holding frame 503, SMA 507 and SMA drive control section 520 correspondsto the drive unit in the present invention. The compensation lens 502corresponds to the driven member in the present invention.

FIG. 20 a shows that application of electric current to the SMA 507 issuspended. In FIG. 20 a, the sliding section 503 a of the holding frame503 holding the compensation lens 502 is engaged slidably with the guiderod 501 mounted on the base 510. Between the sliding section 503 a andbase 510, the SMA 507 and bias spring 508 are connected in such a waythat the forces thereof is applied in the opposite directions. Sinceapplication of power to the SMA 507 is suspended, the holding frame 503,namely, compensation lens 502 is pulled downwardly in the drawing by thebiasing force of the bias spring 508, and is stopped at the SMApower-off position P0 (zero) which is the initial position.

FIG. 20 b shows that the standby current Is(1) is applied to the SMA507, and the compensation lens 502 is moved to the centering position ofthe optical axis of the imaging optical system. In FIG. 20 b, thestandby current Is(1) has been applied to the SMA 507 to contract theSMA 507 in such a way that the resistance Rs(1) of the SMA 507 is equalto the target resistance Rtg(1) of the centering position which is thereference position. Then the holding frame 503, namely, the compensationlens 502 has been moved upwardly in the drawing along the guide rod 501against the biasing force of the bias spring 508, and has been stoppedat the centering position P1.

The position of the compensation lens 502 can be moved to a desiredposition from the centering position P1 for image stabilization bycontrolling the drive current Is(n) while monitoring the resistanceRs(n) of the SMA 507. This requires correction of the hysteresis betweenthe movement from top to bottom and from bottom to top in the drawing.Further, the time needed for movement differs depending on the verticalposition of the compensation lens 502. Thus, similarly to the case ofFIG. 12 in the first embodiment, the settling time for minimizing thetime of movement must be set.

For ease of explanation, an example of the image stabilizing unit 500only for the vertical one-axis direction is shown in the drawing.However, an image stabilizing unit for two axis directions can beimplemented by stacking the same mechanism as that in the presentexample on the image stabilizing unit 500 in such a way that the movingdirections are perpendicular to each other.

FIG. 21 is a flow chart representing an example of the flow of theoperation when the image stabilizing unit 500 as the third embodiment isused in the image pickup apparatus such as a digital camera or mobilephone camera. It should be noted that FIG. 21 shows only the flow of theoperation related to image stabilization. The flow related to the AF orexposure control is not shown in this drawing.

In FIG. 21, when the power of the imaging apparatus is turned on inSteps S801, the ambient temperature Ta is measured according to themethod of calculating the initial resistance Rs(0) of the SMA in StepS803 (status detection step), similarly to the Step S200 “statusdetection subroutine” of FIG. 8 in the first embodiment and the StepS703 of FIG. 19 in the second embodiment. The measured ambienttemperature Ta is used to correct the subsequent operations of the imagestabilizing unit 500, for example, to correct the hysteresis when thecompensation lens 502 is moved to the image stabilization position inthe Steps S811 (to be described later), and to correct the temperaturedependency of the time for movement. This arrangement enhances theperformance of the image stabilizing unit 500.

This is followed by the Step S805 wherein the standby current Is(1) isapplied to the SMA 507 in such a way that the reference positionresistance Rs(1) of the SMA 507 is equal to the target resistance Rtg(1)of the centering position which is the reference position, whereby thecompensation lens 502 is moved from the SMA power-off position P0 (zero)to the centering position P1 (compensation lens centering step). Thepreview operation starts in Step S807 (preview step). In Step S809,verification is made to see whether or not the release switch is fullypressed to be turned on (release detection step). The system waits inStep S809 until the release switch is turned on.

When the release switch has been turned on (Step S809: Yes), the drivecurrent Is(n) of the SMA 507 is controlled in Step S811 in such a waythat the resistance Rs(n) of the SMA 507 is equal to the targetresistance Rtg(n) of the SMA 507 corresponding to the moving distance ofthe compensation lens 502 calculated by the image stabilizing amountcalculating section (not illustrated). Thus, image stabilizationoperation and imaging operation are performed at the same time, wherebythe image data is generated (image stabilizing and imaging step).

In Step S813, verification is made to see whether or not the imagingoperation is terminated (imaging termination check step). If the imagingoperation is not terminated (Step S813: No), the system goes back toStep S803 wherein the ambient temperature Ta is measured. After that,the aforementioned operation is repeated. If the imaging operation isterminated (Step S813: Yes), the imaging apparatus is turned off inSteps S815 and a series of operations terminates.

As described above, according to the third embodiment, a predeterminedinitial current Is(0) is applied to the SMA 507 and the initialresistance Rs(0) of the SMA 507 is detected, whereby the ambienttemperature Ta of the SMA 507 can be detected, without having to installan additional temperature sensor such as a thermistor or a temperaturedetecting circuit for detecting the temperature using the temperaturesensor. This arrangement enhances the performances of the imagestabilizing unit 500, and ensures cost reduction and space saving.

Application of the standby current Is(1) is controlled in such a waythat the reference position resistance Rs(1) of the SMA 507 is equal tothe target resistance Rtg(1) of the centering position, and thecompensation lens 502 is moved from the SMA power-off position P0 (zero)to the centering position P1. This procedure allows the compensationlens 502 to be moved to the centering position P1, without having toadditionally install a sensor or a detecting circuit for detecting theposition of the compensation lens 502. This enhances the performances ofthe image stabilizing unit 500, and ensures cost reduction and spacesaving.

Further, the resistance correction value Rcor(n) is used to correct thehysteresis of the target resistance Rtg(n) of the SMA 507 between themovements of the compensation lens 502 from bottom to top and from topto bottom for image stabilization. This procedure ensures quick movementof the compensation lens 502 to the intended position. Thus, thisarrangement provides an image stabilizing unit 500 of excellentresponse.

In addition, when moving the compensation lens 502 for the purpose ofimage stabilization, the time needed for movement differs according tothe position of the compensation lens 502. Thus, similarly to the caseof FIG. 12 in the first embodiment, the settling time is set up tominimize the time needed for movement, and the compensation lens 502 ismoved by waiting for the minimized settling time. This procedure ensuresquick movement of the compensation lens 502 to the intended position.Thus, this arrangement provides an image stabilizing unit 500 ofexcellent response.

As described above, the embodiment of the present invention provides adisplay unit and drive module using a shape memory alloy as a drivesource, wherein the timing of moving the driven member is controlledbased on the target position to which the driven member is moved, andbased on the settling time until the driven member corresponding to thetarget position is stopped at that position, whereby the driven membercan be moved in the minimum drive time. This arrangement provides thedrive unit and drive module that can be driven at a high speed,independently of the ambient temperature or the position of the drivenmember.

The embodiment of the present invention provides a drive unit and drivemodule using a shape memory alloy as a drive source, wherein apredetermined current is applied to the shape memory alloy, therebycalculating the resistance of the shape memory alloy to which current isapplied, and detecting the ambient temperature of the shape memory alloybased on the calculated resistance. This arrangement provides a driveunit and drive module ensuring accurate detection of the ambienttemperature of the shape memory alloy, without having to installing anadditional temperature sensor.

It is to be expressly understood, however, that the details structureand detailed operations of the components constituting the drive unitand drive module of the present invention can be embodied in a greatnumber of variations with appropriate modification or additions, withoutdeparting from the technological spirit and scope of the inventionclaimed.

1. A drive unit, comprising: a shape memory alloy which is configured tomove a driven member, which is biased in a first direction, in a seconddirection different from the first direction when the shape memory alloyis supplied with electric current; a drive section for supplying theshape memory alloy with electric current; a shape memory alloyresistance calculating section, for calculating a resistance of theshape memory alloy when the shape memory alloy is supplied with theelectric current by the drive section, a status detection section fordetecting a status of the shape memory alloy based on the resistance ofthe shape memory alloy calculated by the shape memory alloy resistancecalculating section, a control section for controlling, based on adetection result of the status detection section, the drive section tocontrol the shape memory alloy to move the driven member.
 2. The driveunit of claim 1, wherein the status detection section includes atemperature detection section for detecting an ambient temperature ofthe shape memory alloy.
 3. The drive unit of claim 2, wherein thecontrol section controls the drive section based on the detected ambienttemperature.
 4. The drive unit of claim 3, wherein the control sectioncontrols the drive section so that the driven member is moved toward afirst position and then is moved toward a second position different fromthe first position, and the control section inserts a settling timedetermined based on the detected ambient temperature, before the drivenmember is moved toward the second position, so as to wait for a movementof the driven member moved toward the first position to settle.
 5. Thedrive unit of claim 1, wherein the status detection section includes aline breakage detecting section for detecting a line breakage or a shortcircuit of the shape memory alloy.
 6. The drive unit of claim 1, whereinthe drive section supplies the shape memory alloy with such an electriccurrent or a voltage that raises a temperature rise of the shape memoryalloy by the electric current is negligible.
 7. The drive unit of claim1, wherein the drive section supplies the shape memory alloy with suchan electric current or a voltage that does not cause a phasetransformation of the shape memory alloy from a martensite phase into anaustenite phase.
 8. The drive unit of claim 2, comprising: a storagesection for storing a value of a temperature rise of the shape memoryalloy caused by electric current of a predetermined value supplied tothe shape memory alloy by the drive section, wherein the temperaturedetection section includes a temperature correction section for anambient temperature detected by the temperature detection section basedon the value of the temperature rise, stored in the storage section, ofthe shape memory alloy caused by the electric current of thepredetermined value.
 9. The drive unit of claim 2, wherein thetemperature detection section detects an ambient temperature of theshape memory alloy before the driven member is moved by the shape memoryalloy.
 10. A drive module, comprising: a driven member which is biasedin a first direction; a shape memory alloy which is configured to movethe driven member in a second direction different from the firstdirection when the shape memory alloy is supplied with electric current;a drive section for supplying the shape memory alloy with electriccurrent; and a shape memory alloy resistance calculating section, forcalculating a resistance of the shape memory alloy when the shape memoryalloy is supplied with the electric current by the drive section, astatus detection section for detecting a status of the shape memoryalloy based on the resistance of the shape memory alloy calculated bythe shape memory alloy resistance calculating section, a control sectionfor controlling, based on a detection result of the status detectionsection, the drive section to control the shape memory alloy to move thedriven member.
 11. The drive module of claim 10, wherein the drivenmember includes an optical system which constitutes an image pickupapparatus.
 12. The drive module of claim 10, wherein the driven memberincludes a shutter blade which constitutes a shutter unit.
 13. The drivemodule of claim 10, wherein the driven member includes a compensationlens which constitutes an image stabilization unit.